Study Of Optical Property And Electrical Property Of CuCr_1-xMg_xO₂（X=0-0.075） Films

CuCrO₂is another hot topic in delafossite materials after CuAlO₂, it has a wideband gap and its energy band structure can also be modified under CMVB （ChemicalModulation of the Valence Band） theory to improve the electric and optical propertiesat the same time. Currently, CuCr_1-xMg_xO₂film has the highest conductivity indelafossite material films, which conductivity can reach220S/cm. Study on CuCrO₂films still in its primary stages, studying the factors that affect CuCrO₂film’sconductive and visible light range transparency is of great significance to realizeartificial controlling optical and electrical properties of CuCrO₂thin films. The filmpreparation method of this article was pulsed laser deposition. Different growthconditions were adopted to ensure visible light transmittance of the film is not reducedin CuCr_1-xMg_xO₂films comparing to CuCrO₂film, where the purpose of doping Mg inCuCrO₂film is to improve the electrical properties of the films. The change of bandstructure affected by Mg doping in CuCrO₂film is highlighted in this work. Carryingstudy of Mg doping affect the film’s band structure in order to understand how Mgdoping change the optical and electrical properties of CuCrO₂thin film.In this paper, Cu2O, Cr2O3and MgO were used as raw materials to prepareCuCr_1-xMg_xO₂ceramic target by high temperature solid state reaction method. Thesepolycrystalline targets are used to deposite films. Polycrystalline targets arecharacterized by XRD, there were no impurity phases being founded in their XRDpatterns. With the increasing of doping amount, the diffraction peak gradually move tolow diffraction angle direction, consistent with theoretical expectation. To find the bestgrowth condition, using pulse laser deposition to prepare CuCr_1-xMg_xO₂（Mg=0-0.075）films by changing one condition while other growth conditions are set. CuCr_1-xMg_xO₂films are characterized by XRD, SEM, I-V curve and visible light transmissionspectrum tests, by comparing the results to set growth temperature as700oC, the laserenergy as200mJ, laser frequency as3Hz and partial oxygen pressure as4.5Pa. Thefilms’ phase structure belong to CuCrO₂3R type structure, no impurity phases appearafter analyzing XRD patterns of Mg doped films, and a series of diffraction peaksappear at （003）,（006）,（009）,（0012） crystal plane, confirming crystals growing alongthe （003） crystal plane orientation. Surface morphology of the doped films werecharacterized by SEM, the films’ grain size is about50nm, with the increase in doping amount the grain size firstly increaseing and then decreaseing.Average visible light transmittance of CuCr_1-xMg_xO₂film falls between70%and85%. Mg doping affected visible light transmittance of the films slightly. By using therelationship between absorption coefficient and the photon energy to predict energyband gap of the film Eg. Eg become smaller while Mg doping amount increase, and themaximum film band gap is2.80eV,0.55eV larger than doped film. CuCr_1-xMg_xO₂film. Indirect absorption coefficients are also calculated which can be used to obtainenergy band structure related to indirect transition. Mg doping affect hybrid degreeamong atoms by changing oxygen octahedral structure in CuCrO₂, as a result changethe band gap of the film.Using conventional four probe method to test films’ I-V curve. Conductivity ofthe film is calculated by thickness correction and edge correction. Mg doping canimprove the conductivity of the film, when the doping amount is0.075theconductivity of the film inceases to a few S/cm, which is1000times larger than that ofCuCrO₂film. The conductivity of the Mg doped films increase as x increasing.Thermal activation energy of the films were obtained by testing films’ conductivitywith variable temperature, confirming Mg can introduce new level to band structure.The activation energy is about0.3eV.